This invention relates to a keytop plate and a method for producing the same.
Conventionally, some electronic devices are used in an environment where invasive dust or moisture is present. Accordingly, push-button switches to be used as a control part for such electronic devices are required to have a construction which prevents invasion of dust or moisture into contact with the switches. In other words, the switches need a dust-proof and moisture-proof or water-proof construction.
In order to meet the above-mentioned requirements, a switching plate for push buttons of a construction shown in FIG. 12 has been proposed. The switching plate for push buttons includes a keytop plate 85 with no through-holes therein disposed above a switch substrate 71, and a casing 95 disposed on the keytop plate 85. The keytop plate 85 is bonded, along its entire periphery C, to the lower surface of the casing 95.
The keytop plate 85 includes a synthetic resin film 87 of polyethylene terephthalate (referred to as "PET" hereinbelow), and a plurality of resin parts 88 molded to the synthetic resin film 87 at predetermined positions, whereby a plurality of keytops 89 are formed. A plurality of switch contacts 73 are disposed on the switch substrate 71 at positions opposite to the respective keytops 89. A click plate 75 is disposed on each of the switch contacts 73.
When any one of the keytops 89 is depressed, the keytop plate 85 is deflected so as to allow the depressed keytop 89 to be lowered. By this, the corresponding click plate 75 is depressed and deformed into a reverse configuration. Simultaneously, the corresponding switch contact 73 is turned on.
Due to the above-mentioned construction, any water droplets, dirt, or dust, having impinged on the casing 95 and/or the-keytop plate 85, may be prevented from getting to the substrate 71. Thus, a water-proof and/or dust-proof property for the switch plate may be obtained.
It is noted, however, that although the synthetic resin film 87 has flexibility and is easily deformed, it has substantially no ductility. Accordingly, and in the case of the prior art example shown in FIG. 12, the synthetic resin film 87 is difficult to deform or deflect when any one of the keytops 89 is depressed so as to be lowered by its depression stroke, since the synthetic resin film 87 is secured, along its periphery C, to the casing 95. This causes a problem in that the keytops are difficult to depress. This problem becomes more significant as the keytops are miniaturized specifically in accordance with miniaturization of electronic devices.
In order to overcome the above mentioned problem, a keytop plate 85-2 of a construction shown in FIG. 13 has been proposed.
The keytop plate 85-2 includes a sheet 87-2 and keytops 89-2. The sheet 87-2 and the keytops 89-2 are integrally molded from silicone rubber. Thus, the keytop plate 85-2 allows the keytops 89-2 to be easily depressed even when the keytop plate 85-2 is securely held along its entire periphery, since silicone rubber may be easily extended.
It is noted, however, that the above-mentioned keytop plate 85-2 provides a relatively soft tactile feeling when any one of the keytops 89-2 is depressed, since the keytops are made from silicone rubber which is flexible by nature. Thus, a hard tactile feeling, which is preferable to most users and which may be provided by molded resin, could not be obtained.
When printing desired markings or characters on the surface of each of the keytops 89-2 of the keytop plate 85-2, such printing operation should be performed directly on the surface of each of the individual keytops 89-2 having a substantially cubic configuration. Such printing operation is complex and less efficient, when compared to a printing operation in which a marking or the like is directly printed on a sheet. It is also difficult to perform a fine printing. It is also noted that, when a plurality of keytops 89-2 are simultaneously printed with a marking, misregistration between the keytops 89-2 and a printing means would occur, since the keytop plate 85 has flexibility. As a result, simultaneous printing of a marking or the like on the keytops 89-2 is impossible. This reduces the efficiency of the printing operation.